1. Field of the Invention
The present invention relates to a paint selector valve which makes it possible to switch the supply and the cutoff of a paint to be supplied to a fluid passage by opening and closing a valve plug by the aid of a pressure fluid.
2. Description of the Related Art
A painting system has been hitherto adopted, for example, to apply electrostatic painting to a painting objective such as a body of an automobile by applying a high voltage to a conductive paint. In such a painting system, the paint, which is supplied from a paint supply source, is supplied via a passage to a coating apparatus such as a spray gun so that the paint is sprayed from the coating apparatus to the painting objective. Usually, a paint selector valve is provided in the passage disposed between the paint supply source and the coating apparatus. The paint selector valve is used to supply and cut off the paint to be supplied to the coating apparatus.
A manifold, which has an outflow passage on the lower side of a casing, is connected to the paint selector valve as described above. A piston, which is provided in the casing, is displaced in an axial direction by the aid of pilot air. A valve shaft, which is connected to the piston, is integrally displaced. A valve section, which is composed of, for example, a resin material, is provided at the lower end of the valve shaft. The valve section is capable of being seated on a valve seat member which is formed at a lower portion of the casing and which is communicated with the outflow passage of the manifold. The valve section is separated from the valve seat member when the paint flows into the casing from an inflow port formed on the side surface of the casing, and thus the paint flows to the outflow passage of the manifold via an outflow port of the valve seat member (see, for example, Japanese Laid-Open Patent Publication No. 2002-243062).
In general, a variety of different paint colors are designated for the painting objectives such as automobiles to be subjected to the painting by using the painting system as described above. Therefore, when the painting is performed with the various different paint colors for the painting objectives, those provided corresponding to the number of the designated painting colors include a plurality of paint supply sections corresponding to the different paint colors, the outflow passages to be connected to the paint supply sections, the paint selector valves, and the coating apparatus. The paints having desired paint colors for the painting objectives are optionally supplied from the paint supply sections via the paint selector valves to the coating apparatus to paint the painting objectives with the desired different paint colors respectively.
However, in the painting system as described above, for example, the paint selector valves, the passages, and the coating apparatus, which correspond to the number and the amounts of the various different paint colors designated for the painting objectives, are required. Therefore, the equipment cost is increased for the painting system, and an extremely large installation space is required.
Therefore, in recent years, in order to simplify the arrangement and suppress the equipment cost of the painting system as described above, the following painting system is adopted. That is, a plurality of paint selector valves are provided for a manifold which has a single outflow passage for allowing the paint to flow therethrough. Further, a single coating apparatus, which is connected to the outflow passage, is provided. In the case of this painting system, the outflow passage and the coating apparatus are commonly used when the paints of the different paint colors flow therethrough and are sprayed.
Only the paint having the desired paint color is supplied from the paint selector valve via the outflow passage to the coating apparatus by allowing only one of the plurality of paint selector valves to be in the valve-open state, and thus the painting objective is painted with the desired paint color by spraying paint from the coating apparatus.
However, when the paint of another paint color is newly supplied to the outflow passage and the coating apparatus to perform the painting, the previous paint remains in the outflow passage and the coating apparatus, because the plurality of paints of the different paint colors are supplied to the single outflow passage and the single coating apparatus. It is necessary to completely remove the paint beforehand by washing, for example.
For example, when the conventional technique concerning Japanese Laid-Open Patent Publication No. 2002-243062 is applied to the painting system as described above, the paint tends to remain in the outflow port of the valve seat member when the valve section of the paint selector valve is seated on the valve seat member, because the valve section seated on the valve seat member is separated from the outflow passage by a predetermined spacing distance. Therefore, when the interior of the outflow passage and the coating apparatus is washed, it is difficult to completely remove the paint remaining in the outflow port. When the paint of another different paint color is supplied to the outflow passage via another paint selector valve, it is feared that the paint may be mixed with the remaining paint.